The present invention relates to an apparatus and method for coating articles with polymers and other materials suitable for coating by vapor deposition. More specifically, the present invention provides an apparatus and method for coating wires and wire-type parts with the polymer parylene by a vapor deposition coating process conducted in a coating apparatus.
Prior art methods of coating articles with polymers include the process of vapor deposition. Parylene is an excellent polymer for coating articles due to its ability to form thin surface films and to conform to articles of various shapes and surface configurations. Parylene is particularly suited for coating wires and wire-type parts of various lengths and diameters due to such coating properties. Parylene is typically applied to the surfaces of articles by the process of vapor deposition conducted under vacuum conditions in a coating apparatus. The parylene dimer is first vaporized to a gaseous state and then pyrolitically cleaved to form reactive monomer parylene vapors. The monomer parylene vapors are transferred to and circulate within a coating chamber of the coating apparatus in which articles to be coated are contained. As the monomer vapors contact the surfaces of the articles, the vapors condense on the surfaces and polymerize to form a surface film or coating of parylene on the articles. Such a deposition coating process is an excellent method of coating wire-type articles and wire parts on which even surface films or coatings are difficult to achieve. This is particularly the case when coating when coating large quantities or bulk loads of wire-type articles and wire parts by a vapor deposition process.
Prior art devices for coating articles by vapor deposition include a drum-type apparatus, as disclosed in U.S. Pat. No. 4,758,288, wherein articles are placed in a coating drum which rotates and tumbles articles during the coating process. A disadvantage of this coating apparatus is that parylene vapors must be introduced into the drum by means of a feed tube. As the vapor deposition coating process is conducted under vacuum conditions, pressure gradients may be created within the drum and also between the drum and the external atmosphere in which parylene vapors circulate. Pressure gradients cause an uneven circulation of parylene vapors which results in uneven depositing of parylene vapors on the surfaces of articles and uneven and inconsistent surface films. In addition, the coating apparatus is not conducive to coating large quantities or bulk loads of articles due to mechanical damage to surface films cause by the weight of large quantities or bulk loads.
The basket-type cellular apparatus disclosed in U.S. Pat. No. 5,201,956, assigned to the assignee of the present application, is an improvement upon the drum-type apparatus, wherein a plurality of basket-type cells with multiple side wall through holes are configured about a common axis of rotation. The side wall through holes put articles contained therein in close communication with circulating parylene vapors as the basket-type cells are rotated during the coating process. Although an improvement over prior art devices, the basket-type cellular apparatus is not by itself always a suitable means for coating large quantities or bulk loads of articles, particularly large or bulk loads of wire-type articles and wire parts..
Other prior art devices for coating wire-type articles and wire parts by parylene vapor deposition include manually mounting individual articles in a static position to a fixture plate contained within a coating chamber of a coating apparatus. For example, mounting wire parts to the fixture plate enables individual wire parts to hang freely, exposing the surfaces of the wire parts to parylene vapors which circulate in the atmosphere within the coating chamber. However, the wire parts must be sufficiently spaced apart to prevent adjacent wire parts from touching or adhering together. Insufficient space between individual wire parts can cause an uneven deposition of parylene which forms inconsistent surface films on the wire parts or results in portions of the surfaces of the wire parts to remain uncoated. The spatial arrangement required insure thorough and even parylene deposition and ultimately even and consistent surface films or coatings involves significant manual handling and fixturing to appropriately space and mount individual wire parts to the fixture plate. Manually mounting and removing individual wire parts in this manner is a labor intensive practice which reduces the efficiency of this coating process.
As a result, the use of a device such as the fixture plate to properly arrange wire parts for deposition coating results in a low parts per load ratio. This coating process is also a static method of coating, wherein the wire parts remain stationary during the coating process. Such a static process, therefore, is highly dependent upon achieving an adequate circulation of parylene vapors and susceptible to pressure gradients which may occur in the atmosphere of the coating apparatus.
Therefore, it is desirable to have a vapor deposition coating apparatus and method which reduces or eliminates the need for manual handling and fixturing of articles, and which increases the parts per load ratio of prior art devices, particularly with respect to coating wire-type articles and wire parts. In addition, it is also desirable to reduce the susceptibility of the coating apparatus and method to pressure gradients during the coating process by adequately exposing the surfaces of the articles to be coated, while preventing the articles from sticking or becoming coated together. In addition, it is desirable to provide a vapor deposition coating apparatus and method for surface coating large quantities or bulk loads of articles, and particularly large quantities or bulk loads of wire-type articles and wire parts, which produces even and consistent surface films.
Embodiments of the present invention provide an apparatus and method for coating articles and, in particular, for coating large quantities or bulk loads of articles, including wire-type articles and wire parts, by a process of vapor deposition which overcomes the problems of prior art devices and methods described above.
In a first embodiment of the present invention, a mobile cellular tumble coater is provided for coating wire parts by a process of vapor deposition conducted under vacuum conditions within a coating apparatus. The mobile cellular tumble coater is positioned within a coating chamber of the coating apparatus, wherein parylene vapors are circulated to coat wire parts contained in the mobile cellular tumble coater. Parylene vapors circulate through the atmosphere of the coating chamber and the mobile cellular tumble coater and, upon contact with surfaces of wire parts, condense and polymerize on surfaces of wire parts to produce parylene surface coats. During the vapor deposition process, the mobile cellular tumble coater rotates and tumbles causing wire parts contained therein to be maintained in a sufficiently mobile state during the coating process such that wire parts are prevented from sticking together or becoming coated together by parylene deposition.
In a first embodiment of the present invention, the mobile cellular tumble coater includes at least one mobile part cell and an inner support base to which the mobile part cell is disposed. The mobile part cell includes a hollow portion with a first terminal end and a second terminal end and an outer wall connecting each terminal end. The hollow portion of the mobile part cell may be constructed as a circular cylinder. The outer wall of the hollow portion has multiple through holes which are large enough to allow vapors of coating material to flow into the mobile part cell, yet small enough to contain wire parts to be coated. The hollow portion may be constructed of metal screening or other suitable materials which have the properties to withstand the conditions of the vapor deposition coating process, such as, but not limited to, wire mesh, high-density polyethylene, polyvinylchloride, polyurethane and nylon. The gauge of the screening may be increased or decreased to accommodate the size of wire parts to be coated.
At least one of the terminal ends of the hollow portion of the mobile part cell includes an end cap that is removably attached to the mobile part cell and permits loading and unloading of wire parts. The end cap may be constructed for complete removal from the mobile part cell or may be attached to the mobile part cell by hinges. The end cap is constructed of high-density polyethylene or other suitable materials which have the properties to withstand the conditions of the vapor deposition coating process, such as, but not limited to, polyvinylchloride, polyurethane and nylon.
The inner support base of the mobile cellular tumble coater includes a hollow cylindrical chamber with a larger overall dimension than the mobile part cell to which the mobile part cell is disposed. The hollow chamber may be constructed and arranged as a circular cylinder similar to the mobile part cell and constructed of porous or solid material suitable to withstand the conditions of the vapor deposition process. Alternatively, the hollow chamber may comprise multiple through holes large enough to permit the flow of vapors of coating material through the hollow chamber to enhance circulation of vapors throughout the coating chamber and the mobile part cell.
The mobile cellular tumble coater further includes a mechanism to rotate the inner support base and the mobile part cell disposed thereon. The mechanism may include a drive motor and drive shaft which is rigidly connected at a first terminal end to the inner support base and passes through the coating chamber and a vacuum seal to connect to the drive motor at an opposite terminal end. The drive motor turns the drive shaft which causes the inner support base to rotate within the coating chamber.
In the first embodiment of the present invention, the mobile part cell is removably attached to an outer surface of the inner support base by at least two attachment devices, such as, but not limited to, a pair of cables. A first terminal end of each cable is connected adjacent to the first or the second terminal end of the mobile part cell. A second terminal end of each cable is attached to the outer surface of the inner support base in such a manner that the cable permits the mobile part cell to move and swing away from the inner support base. Each cable may be attached to the inner support base by a loop or hook-like connection that permits the cable to move and swing from its point of attachment to the inner support base, thereby swinging or propelling the mobile part cell away from the inner support base.
The cables and other similar attachment devices permit easy detachment and reattachment of the mobile part cell from the inner support base for loading articles into the mobile part cell. Other attachment devices may include, but are not limited to, hinges, wires and rods. The attachment devices are constructed of rigid, inflexible material which has the properties to withstand the conditions of the vapor deposition process.
When attached to the inner support base, the mobile part cell rotates from a fixed position on the inner support base as the inner support base is rotated by the drive shaft. The rigid and inflexible nature of the cables permits the mobile part cell to swing or be propelled away from the inner support base. The loop or hook-line connection which attaches each cable to the inner support base facilitates such movement of the mobile part cell away from the inner support base. Without a rigid and inflexible nature, the cables would buckle and collapse under the weight of the mobile part cell and cause the mobile part cell to roll and slide on the inner support base in a relaxed position, rather than swing or be propelled away from the inner support base.
The deposition coating process begins with the vaporization and pyrolization of parylene. Although more stable as a dimer, parylene must be initially vaporized and then pyrolytically cleaved into monomer vapors prior to circulating throughout the coating chamber of the coating apparatus. Parylene is vaporized and pyrolized by methods that are well known to those of ordinary skill in the art. Parylene is vaporized and pyrolized to monomer vapors by the method disclosed in U.S. Pat. No. 5,201,956, incorporated herein by reference.
Monomer parylene vapors are transferred to the coating chamber of the coating apparatus in which the mobile cellular tumble coater is positioned and circulate throughout the atmosphere of the coating chamber and the mobile cellular tumble coater. In the first embodiment, the rotation of the inner support base causes the mobile part cell attached thereon to rotate from a fixed position on the inner support base. As the inner support base rotates, the mobile part cell swings from or is propelled away from the inner support base. The mobile part cell rotates upward in a circular arc until reaching just past a top or uppermost point of the circular arc, wherein the mobile part cell begins to rotate downward. As the mobile part cell rotates downward, it is propelled away from the inner support base until reaching a point at which it moves increasingly inward toward the inner support base and eventually collides with the inner support base.
The collision of the mobile part cell with the inner support base mechanically jars the mobile part cell, causing wire parts contained therein to vibrate and tumble. Such mechanical agitation separates and reorients wire parts, and maintains wire parts in a sufficiently mobile state during the coating process to prevent wire parts from sticking or becoming coated together. Mechanical agitation also insures that surfaces of individual wire parts will be sufficiently exposed to circulating parylene vapors during the coating process to produce even and consistent surface coats.
In another embodiment of the invention, the mobile part cell is removably attached by at least one pair of cables to an inner surface of the inner support base. The mobile part cell is propelled away from the inner support base as the inner support base rotates. The mobile part cell rotates upward in a circular arc, as described in the first embodiment, until reaching just past a top or uppermost point of the circular arc, wherein the mobile part cell begins to rotate downward. As the mobile part cell rotates downward, it is propelled away from the inner support base until reaching a point at which it moves increasingly inward toward the inner support base and collides with the inner support base. Collision of the mobile part cell with the inner support base creates the mechanical agitation necessary to maintain the wire parts contained within the mobile part cell in a sufficiently mobile state during the coating process to prevent the wire parts from sticking or becoming coated together.
In still another embodiment of the invention, the mobile part cell is contained within at least one carrier cell that has a larger overall dimension than the mobile part cell and is rigidly attached to the inner surface of the inner support base. The mobile part cell is not fixed or attached to the carrier cell, but, rather, is freely contained within the carrier cell. As the inner support base rotates, the carrier cell rotates from a fixed position on the inner support base, and the mobile part cell contained therein rolls and tumbles about the carrier cell.
As the mobile part cell rolls and tumbles about the carrier cell, it is mechanically agitated by at least one pair of cleats. The pair of cleats includes a first cleat mounted on the outer surface of the inner support base and a second cleat coupled to a surface of an inner wall of the coating chamber. The first cleat rotates from a fixed position on the inner support base and momentarily engages or rests upon the second cleat when the first cleat meets the second cleat. The first cleat immediately disengages or slips from the second cleat as the first cleat continues to rotate from rotation of the inner support base. The disengagement or slipping of the first cleat from the second cleat mechanically jars the carrier cell and the mobile part cell contained therein such that wire parts contained within the mobile part cell are maintained in a sufficiently mobile state and prevented from sticking or becoming coated together.
The inner support base may include an end plate that is attached at the first terminal end and the second terminal end of the hollow chamber to enclosed the carrier cell and the mobile part cell contained therein.
In yet another embodiment of the invention, the mobile part cell is contained within a carrier cell having at least one cell cleat rigidly attached to an inner wall surface of the carrier cell. As the carrier cell rotates from a fixed position on the inner support base, the mobile part cell engages or rests upon the cell cleat. As the carrier cell rotates, the mobile part cell is lifted upward by the cell cleat. When the carrier cell begins to rotate downward, the mobile part cell disengages or falls from the cell cleat and collides against the inner wall surface of the carrier cell. The collision of the mobile part cell with the carrier cell mechanically jars the mobile part cell which maintains wire parts contained therein in a sufficiently mobile state during the coating process.
Similarly, the first and the second terminal ends of the hollow chamber of the inner support base may be sealed with end plates to enclose the carrier cell and mobile part cell contained within the hollow chamber.
The mobile cellular tumble coater may be scaled upward by attaching a plurality of mobile part cells to the inner support base during a single coating run, to achieve a high parts per load ratio. The mobile cellular tumble coater may coat large quantities or bulk loads of wire parts by increasing the diameter of the inner support base and the size of the coating chamber to accommodate a plurality of mobile part cells or larger-sized mobile part cells. Mobile part cells may contain wire parts of a variety of lengths and diameters during a single run, thereby increasing the economy of the mobile cellular tumble coater. In addition, individual mobile part cells may be divided into subcompartments for containing a variety of sizes of wire parts further increasing the economy of the mobile cellular tumble coater.